GB2575095A

GB2575095A - Tablet tool coating

Info

Publication number: GB2575095A
Application number: GB201810695A
Authority: GB
Inventors: John Blanchard Robert; Kenneth Southall Wayne
Original assignee: Teer Coatings Ltd; I Holland Ltd
Current assignee: Teer Coatings Ltd; I Holland Ltd
Priority date: 2018-06-29
Filing date: 2018-06-29
Publication date: 2020-01-01
Anticipated expiration: 2038-06-29
Also published as: GB201810695D0; GB2575095B

Abstract

A method of coating a steel tablet tool 30 comprising: applying a first inner chromium adhesion layer 32; a second chromium nitride layer 34; a third transition layer 36 of chromium, nitrogen and aluminium with the concentration of aluminium increasing outwardly; and a fourth outer layer 38 of chromium, nitrogen and aluminium. The concentration of nitrogen in the second layer 34 may increase outwardly through the layer to gradually increase the hardness of the coating; the nitrogen concentration may increase only in an inner part of the second layer which may extend for less than 50% of the thickness of the second layer 34. The nitrogen concentration in the third layer 36 may decrease outwardly. The coating may be applied using closed field unbalanced magnetron sputtering with a maximum process temperature of 300-500 °C and using four or six magnetrons, with chromium targets on at least two magnetrons and aluminium targets on at least two magnetrons. A coated tablet tool produced by said method is also disclosed. The invention is intended to increase the resistance of tablet press tools to abrasion, extending their useable lifespan.

Description

Tablet Tool Coating

This invention concerns a method of coating a steel tablet tool, and a tablet tool coated by such a method.

In tablet presses a number of tools or punches are provided which are used to press powder into a tablet of a required shape, with a required finish and perhaps also a marking formed by the tip of the tool. It is often required to provide a coating on the tool to increase the longevity of the tool, to reduce corrosion or wear of the tool, and/or to avoid sticking of the powder to the tool.

Tablet press tools are considered as consumable products. Their lifespan of usage is different for each tablet manufacturer. The number of tablets each tool can manufacture is dependent upon factors such as the roughness of a granule and its abrasive effects on the tooling, the pressure that is applied to the tooling in the tablet press in order to form the tablet and also the care and attention that the tooling is treated with by the customer. When the tooling is worn or damaged and can no longer produce tablets of the quality the customer require the tools will be discarded, this can affect a customer’s productivity and profitability.

The present invention concerns the application of a hard coating to the tooling that is much harder than the materials that the tablets are made from and therefore resists abrasion through usage. This protects the delicate design and features of the tooling increasing the usable lifespan benefiting the customer.

Physical Vapour Deposition (PVD) is a method for applying coatings. Typically such a process will be carried out at a relatively high process temperature within the range of 300°C to 500°C.

A particular physical vapour deposition technique is closed field unbalanced magnetron sputtering, as described in for instance UK patent specification no. 2462890 and European patent specification no. 0521045. This technique can be used either for reactive or non-reactive coatings. This technique can be used for applying thick abrasion resistant hard coatings such as CrALN.

All percentages in this specification are to be to understand as atomic or mol percentages.

According to a first aspect of the invention there is provided a method of coating a steel tablet tool, the method comprising applying a first inner Chromium adhesion layer followed by a second Chromium Nitride layer, this is followed by a third transition layer of Chromium, Nitrogen and Aluminium, with the concentration of aluminium increasing outwardly, and followed by a fourth outer layer of Chromium, Nitrogen and Aluminium.

The first inner layer may have a thickness of between 0.1 pm and 0.5pm and is used to promote the adhesion of the coating to the substrate and also the adhesion of the hard coating to the Chromium adhesion layer.

The concentration of Nitrogen in the second layer may increase outwardly through the layer to gradually increase the hardness of the coating to between 1600Hv to 2100Hv without introducing stress into the coating. The concentration of Nitrogen may increase only in an inner part of the second layer, which inner part may extend for less than 50% and potentially less than 30% of the thickness of the second layer.

The second layer may have a thickness in the range of 0.2pm to 1,5pm. The minimum concentration of Nitrogen in any part of the second layer may be 5%, and the maximum Nitrogen concentration in any part of the second layer may be 65%.

The Nitrogen concentration may decrease outwardly in the third layer. The thickness of the third layer may be between 1 .0pm and 2.0pm.

The concentration of Nitrogen in the third layer may be between 60% and 70% at an inner part of the third layer, and between 30% and 40% at an outer part of the third layer. The concentration of aluminium in the third layer may be 0% to 25%, and the concentration of Aluminium in an outer part of the third layer may be 15% to 25%. The concentration of Chromium in the third layer may be 25% to 35%. The increase in Aluminium Concentration increases the hardness of the coating to between 2000Hv to 3000Hv, thus increasing the wear resistance of the coating matrix already applied.

The thickness of the fourth layer may be between 3.0pm and 5.0pm. The relative concentrations of Chromium, Aluminium and Nitrogen in the fourth layer may be stable across the layer. The concentration of Chromium in the fourth layer may be 25% to 35%. The concentration of Aluminium in the fourth layer may be 15% to 25%. The concentration of Nitrogen in the fourth layer may be 60% to 70%. The coating layers may be applied using closed field unbalanced magnetron sputtering, with a maximum process temperature of 300°C to 500°C.

The sputtering may be carried out with four or six magnetrons, with Chromium targets on at least 2 magnetrons and Aluminium targets on at least 2 magnetrons. The strength of these magnetrons are tailored to suit the appropriate sputter materials.

The tablet tools are preferably held in a jig during coating, and the jig may hold the tablet tools about a central part thereof. The punch tips may face towards the sputter sources and may be rotated during coating to ensure an even coating thickness over the punch tip face and outside diameter.

Coating of the tablet tool may take place in a vacuum chamber where the pressure may be reduced to less than 5.0x10^-5 torr.

A pulsed DC power is preferably applied to the bias, and the pulse voltage may vary between 40V and 90V.

The power applied to the targets may vary between 3.0kW and 6.0kW. The sputtering may take place in a reduced pressure argon atmosphere, and the reduced pressure may be between 0.7 x 10^-4 torr and 3.0 x 10^-3 torr, and more particularly in a range between 1.0x10^-4 torr and 1.0 x 10^-3 torr.

An Ion clean of the tool may be carried out prior to providing a coating layer on the tooling, and this may be done by applying a voltage in the range of 400V to 600V on the bias. Preferably the bias power supply will have settings of between 150KHz to 300KHz and a duty cycle of between 500ns to 1500ns.

The coating may have a total thickness of between 4pm and 9pm.

According to a further aspect of the invention, there is provided a coated tablet tool, the tablet being coated by a method according to any of the preceding fifteen paragraphs.

The tablet tool may be made of cold formable tool steel.

An embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings, in which:

Fig. 1 is an SME image of a prior art coating;

Fig. 2 is a similar view to Fig. 1, but of a coating according to the invention;

Fig. 3 is a diagrammatic plan view of physical vapour deposition apparatus useable with methods according to the invention; and

Fig. 4 is a diagrammatic sectional view through a tablet punch with a coating according to the invention.

The prior art coating shown in Fig. 1, has a typical coating thickness of less than 4pm.

A plurality of cold formable tool steel tablet punches 30 may be coated with a Chromium, Aluminium and Nitrogen coating by the following method. A physical vapour deposition apparatus 10 using closed field unbalanced magnetron sputtering is used. Fig. 3 shows the apparatus 10 with four or 6 equispaced magnetrons. The closed magnetic field lines 18 are illustrated, and an argon source 20 is shown.

The jigs 16 are set up to hold the punches such that the punches are coated on the tip only, and a number of test disc are mounted in the system to facilitate testing. The jigs 16 and contents are cleaned in a solvent cleaning line with ultrasonic cleaning, vapour drying and vacuum drying.

The jigs 16 and tools are cleaned with an anti-static Nitrogen gun, and the chamber has previously been cleaned with this gun. The jigs 16 are located in the apparatus 10 with a vacuum chamber, and the pressure is reduced to less than 5.0 x 10^-5 torr. A “rate of rise” check is made to check for the vacuum seal within the chamber. Prior to the bonding layer being applied an Ion Clean on the punches is carried out to ensure that they are in a clean state prior to the adhesion layer being applied. This is followed by inner bonding layer of pure Chromium which is applied to the tools with no Nitrogen present. This acts as an adhesion layer onto the steel. A first inner coating layer with a thickness of between 0.1 pm and 0.5pm is then formed.

The following parameters are applied to the sputtering during formation of the first coating layer. The target power is between 3.0kW and 6.0kW. The bias power is between 40V and 70V. The bias pulse settings are between 200kHz and 300kHz and 500 Ns to 1500 Ns. The coating is carried out in a reduced pressure Argon atmosphere, at a pressure of around 1.0 x 10^-3 torr.

The first inner coating layer 32 is of Chromium and has a thickness of between 0.1pm and 0.5pm. The inner coating layer 32 promotes adhesion of the coating on the punches 30. This layer 32 also promotes adhesion of subsequent coating layers on to the punches 30.

A second coating layer 34 with a thickness of between 1.0pm and 1.5 pm is formed, in which the amount of Nitrogen is increased outwardly from around 5% to 65%. The amount of Nitrogen increases for about the inner 25% of the second coating layer 34, and then remains constant for the remainder of the second coating layer 34.

The conditions in which the second layer 34 is applied by sputtering is with a target power of between 3.0kW and 5.0kW. There is a bias power of between 40V and 90V. The bias pulse settings are between 200kHz and 300kHz and 500Ns to 1500Ns. The Argon atmosphere is again at a pressure of around 1.0 x 10’³ torr.

A third coating layer 36 is formed with a thickness of between 1.0 pm and 2.0pm. During this phase the Aluminium targets are increased in power from zero to between 3.0kw and 6.0kw. The third outer coating layer 36 is produced by sputtering with the following conditions. A target power of between 3.0kW and 6.0kW, a bias power of between 40V and 90V. The bias pulse settings are between 200kHz and 300kHz and 500Ns to 1500Ns. The Argon pressure is again around 1.0x10^-3 torr. Initially the Nitrogen level is at 60% to 70% but is reduced during the course of this coating to 30% to 40%. The coating takes place overall for between 3 and 6 hours.

A fourth outer layer 38 is formed with constant proportions of Chromium, Aluminium and Nitrogen across the layer, and the following proportions are used: Nitrogen 60% to 70%, Aluminium 15% to 25%, and Chromium 25% to 35%. This is applied for a period of between 2 and 4 hours to achieve an overall thickness of the coating of between 4 and 9 microns.

The coated punch 30 is shown diagrammatically in Fig. 4. An SEM in shown in Fig. 2 illustrating a coating thickness of greater than 4pm. The SEM also shows that the coating still has a fully dense glassy like structure, as opposed for instance to a columnar structure.

This multi-layer coating provides a coating which has good abrasive and adhesive wear resistance. The combination of high process temperature and the closed field system used with the PVD technique results in a fully dense coating.

The first inner adhesion layer promotes adhesion of the overall coating on the substrate, and also adhesion of the hard coating of the second, third and fourth layers to the adhesion layer. The increase of the Nitrogen concentration in the second layer increases the hardness of the coating without introducing stress into the coating. In the third layer the increase in Aluminium increases the hardness of the coating, and thus increases wear resistance.

It is to be realised that a wide range of variations may be made without departing from the scope of the invention. For instance different materials and/or conditions may be applied. Rather than four magnetrons, sputtering may be carried out with for instances six magnetrons.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A method of coating a steel tablet tool, the method comprising applying a first inner Chromium adhesion layer followed by a second Chromium Nitride layer, this is followed by a third transition layer of Chromium, Nitrogen and Aluminium, with the concentration of aluminium increasing outwardly, and followed by a fourth outer layer of Chromium, Nitrogen and Aluminium.

2. A method according to claim 1, in which the first inner layer has a thickness of between 0.1 pm and 0.5pm.

3. A method according to claims 1 or 2, in which the concentration of Nitrogen in the second layer increases outwardly through the layer to gradually increase the hardness of the coating.

4. A method according to claim 3, in which the concentration of Nitrogen increases only in an inner part of the second layer.

5. A method according to claim 4, in which the inner part of the second layers extends for less than 50% of the thickness of the second layer.

6. A method according to any of the preceding claims, in which the second layer has a thickness in the range of 0.2pm to 1,5pm.

7. A method according to any of the preceding claims, in which the minimum concentration of Nitrogen in any part of the second layer is 5%, and the maximum Nitrogen concentration in any part of the second layer is 65%.

8. A method according to any of the preceding claims, in which the Nitrogen concentration decreases outwardly in the third layer.

9. A method according to any of the preceding claims, in which the thickness of the third layer is between 1.0pm and 2.0pm.

10. A method according to any of the preceding claims, in which the concentration of Nitrogen in the third layer is between 60% and 70% at an inner part of the third layer, and between 30% and 40% at an outer part of the third layer.

11. A metehod according to any of the preceding claims, in which the concentration of aluminium in the third layer is 0% to 25%, and the concentration of Aluminium in an outer part of the third layer is 15% to 25%.

12. A method according to any of the preceding claims, in which the concentration of Chromium in the third layer may be 25% to 35%. The increase in Aluminium Concentration increases the hardness of the coating to between 2000Hv to 3000Hv, thus increasing the wear resistance of the coating matrix already applied.

13. A method according to any of the preceding claims, in which the thickness of the fourth layer is between 3.0pm and 5.0pm.

14. A method according to any of the preceding claims, in which the concentration of Chromium in the fourth layer is 25% to 35%, the concentration of Aluminium in the fourth layer is 15% to 25%, and the concentration of Nitrogen in the fourth layer is 60% to 70%.

15. A method according to any of the preceding claims, in which the coating layers are applied using closed field unbalanced magnetron sputtering, with a maximum process temperature of 300°C to 500°C, and the sputtering is carried out with four or six magnetrons, with Chromium targets on at least 2 magnetrons and Aluminium targets on at least 2 magnetrons.

16. A method according to claim 15, in which the tablet tools are held in a jig during coating, and the jig holds the tablet tools about a central part thereof.

17. A method according to claim 16, in which the punch tips face towards the sputter sources and are rotated during coating to ensure an even coating thickness over the punch tip face and outside diameter.

18. A method according to any of claims 15 to 17, in which coating of the tablet tool takes place in a vacuum chamber where the pressure may be reduced to less than 5.0x10-5 torr.

19. A method according to any of claims 15 to 18, in which a pulsed DC power is applied to the bias, and the pulse voltage varies between 40V and 90V.

20. A method according to any of claims 15 to 19, in which the power applied to the targets varies between 3.0kW and 6.0kW.

21. A method according to any of claims 15 to 20, in which the sputtering takes place in a reduced pressure argon atmosphere, and the reduced pressure may be between 0.7 x 10-4 torr and 3.0 x 10-3 torr, and more particularly in a range between 1.0 x 10’4 torr and 1.0 x 10’3 torr.

22. A method according to any of claims 15 to 21, in which an Ion clean of the tool is carried out prior to providing a coating layer on the tooling, by applying a voltage in the range of 400V to 600V on the bias.

23. A method according to any of claims 15 to 22, in which the bias power supply will have settings of between 150KHz to 300KHz and a duty cycle of between 500ns to 1500ns.

24. A coated tablet tool, the tablet being coated by a method according to any of the preceding claims.

01 07 19

24. A method according to any of the preceding claims, in which the coating has a total thickness of between 4pm and 9pm.

25. A coated tablet tool, the tablet being coated by a method according to 5 any of the preceding claims.

28 11 18

Amendments to the claims have been filed as follows:

1. A method of coating a steel tablet tool, the method comprising applying a first inner Chromium adhesion layer followed by a second Chromium Nitride layer, this is followed by a third transition layer of Chromium, Nitrogen and Aluminium, with the concentration of aluminium increasing outwardly, and followed by a fourth outer layer of Chromium, Nitrogen and Aluminium, in which the Nitrogen concentration decreases outwardly in the third layer.

8. A method according to any of the preceding claims, in which the thickness of the third layer is between 1.0pm and 2.0pm.

9. A method according to any of the preceding claims, in which the concentration of Nitrogen in the third layer is between 60% and 70% at an inner part of the third layer, and between 30% and 40% at an outer part of the third layer.

10. A method according to any of the preceding claims, in which the concentration of aluminium in the third layer is 0% to 25%, and the concentration of Aluminium in an outer part of the third layer is 15% to 25%.

11. A method according to any of the preceding claims, in which the concentration of Chromium in the third layer may be 25% to 35%. The increase in Aluminium Concentration increases the hardness of the coating to between 2000Hv to 3000Hv, thus increasing the wear resistance of the coating matrix already applied.

12. A method according to any of the preceding claims, in which the thickness of the fourth layer is between 3.0pm and 5.0pm.

13. A method according to any of the preceding claims, in which the concentration of Chromium in the fourth layer is 25% to 35%, the concentration of Aluminium in the fourth layer is 15% to 25%, and the concentration of Nitrogen in the fourth layer is 60% to 70%.

14. A method according to any of the preceding claims, in which the coating layers are applied using closed field unbalanced magnetron sputtering, with a maximum process temperature of 300°C to 500°C, and the sputtering is carried out with four or six magnetrons, with Chromium targets on at least 2 magnetrons and Aluminium targets on at least 2 magnetrons.

15. A method according to claim 14, in which the tablet tools are held in a jig during coating, and the jig holds the tablet tools about a central part thereof.

16. A method according to claim 15, in which the punch tips face towards the sputter sources and are rotated during coating to ensure an even coating thickness over the punch tip face and outside diameter.

17. A method according to any of claims 14 to 16, in which coating of the tablet tool takes place in a vacuum chamber where the pressure may be reduced to less than 5.0x10-5 torr.

18. A method according to any of claims 14 to 17, in which a pulsed DC power is applied to the bias, and the pulse voltage varies between 40V and 90V.

19. A method according to any of claims 14 to 18, in which the power applied to the targets varies between 3.0kW and 6.0kW.

20. A method according to any of claims 14 to 19, in which the sputtering takes place in a reduced pressure argon atmosphere, and the reduced pressure may be between 0.7 x 10-4 torr and 3.0 x 10-3 torr, and more particularly in a range between 1.0 x 10’4 torr and 1.0 x 10’3 torr.

21. A method according to any of claims 14 to 20, in which an Ion clean of the tool is carried out prior to providing a coating layer on the tooling, by applying a voltage in the range of 400V to 600V on the bias.

22. A method according to any of claims 14 to 21, in which the bias power supply will have settings of between 150KHz to 300KHz and a duty cycle of between 500ns to 1500ns.

23. A method according to any of the preceding claims, in which the coating has a total thickness of between 4pm and 9pm.