GB2166363A - Mixer head - Google Patents

Abstract

A mixer head 1, particularly for multi-component polymer systems, for attachment to a suitable metering or dispensing machine 5, comprises a mixing chamber 2 having a rotatable screw member 3, inlets 6, 7 for the materials to be mixed, and an outlet 8 for the mixed material. The screw member 3 may have gaps in the helical threads 9, and may be provided with an angled and grooved tip. <IMAGE>

Description

SPECIFICATION Mixer head This invention relates to a mixer head particularly but not exclusively for multi-component polymer systems.

Various meter/mix/dispense machines are commercially available. These are employed to proportion the separate components of multi-component reactive polymer materials, e.g. epoxy resin, polyurethane, silicone rubber, etc., and mix them together in the correct ratios ready for application.

The metered components are led into a mixing chamber or head where mixing takes place. The mixing is usually achieved by rotating a spindle, with pins protruding from it, at high speed in the chamber. The energy put into the rotation converts to heat which raises the temperature of the polymer mixture, thereby shortening its pot life or gel time. This is a disadvantage.

More recently, static mixers have been introduced and these work by repeatedly dividing the stream of the components within a tube, thus creating a turbulent flow. These waste a considerable amount of material at the beginning and end of operation due to the large volume of polymer contained within the tube, the pot life of which expires before use.

To overcome these problems, we have developed a new type of mixer head which works on the screw principle used in injection moulding machines. In injection moulding the screw is used principally to feed molten thermoplastic material forward towards the injection nozzle at the mould.

It is known that a certain amount of mixing takes place also, and in the present invention this mixing action has been exploited.

Accordingly, the present invention in one aspect provides a mixer head, particularly for multi-component polymer systems, for attachment to any suitable metering or dispensing machine, which comprises a mixing chamber containing or provided with a rotatable screw thread and having inlet means for the components to be mixed and an outlet means for the mixed material.

The invention in another aspect provides a method of mixing multi-component polymer systems, comprising feeding at least two components to be mixed to a mixer head according to the first aspect of the invention, and rotating the screw thread to mix the said components and convey the mixed material to the mixing chamber outlet.

The speed of revolution of the dynamic mixer according to the present invention is relatively slow, i.e. from about 50 to 300 r.p.m. as opposed to about 1,200 r.p.m. for the pin type mixer. Very little heat is therefore produced and this is dissipated by the large bulk of the screw so that negligible temperature rise occurs. Furthermore the volume of materials in the mixer head is at a minimum compared with other systems due to the shallow thread of the screw.

The mixer head according to the invention can cope with components of widely differing viscosities including pastes which a static mixer cannot handle successfully. It also ensures that earlier mixed material is wiped clear of the chamber walls and fed out of the nozzle first. Aged mixture cannot accumulate in the head as may occur with other mixers.

Hardener components are usually fed into the mixer head at the back end of the screw, ensuring that the bearings and seals are kept awash with hardener which cannot react and set on its own. A resin component may be introduced further along the screw and measures may be taken to ensure that the resin only moves in a forward direction.

Alternatively, in a preferred embodiment, cuts may be made through the thread to permit a degree of back flow. This relieves suction at the inlets which can otherwise cause cavitation, or even override the spring action of one-way check valves on the dispenser, thereby upsetting the metered mixing ratio.

Various configurations of screw and thread design are possible, giving different degrees of mixing. Different arrangements are possible for different types of mixtures, e.g. two low viscosity liquids require a different screw pattern from that for two paste materials.

The mixture head can be attached to any metering type dispenser or pump not already fitted with a mixer. For example, a mixer head according to the invention can be advantageously fitted to a Glenmarc Portionator MBT metering/dispensing apparatus manufactured by Glenmarc Manufacturing Inc., but the mixer head of the invention could also be used as an independent mixer fed from two or more pail pumps, for example. The mixer head of the invention may be attached or operated in any plane, e.g. horizontally, vertically or angled, and vertically arranged mixer heads give the advantage that air within the head may be readily purged by the ingress materials. Drive is initially preferably by air motor controlled by an air balance valve which is activated by the operating handle of the metering machine.This ensures that the mixer only rotates when materials are being fed into it, thereby preventing overheating of the polymers or cavitation which could aerate the mixture.

Air-free mixed materials emerge from the nozzle at the front end of the mixing chamber.

Other forms of motor drive may be used, including electric and hydraulic motors with suitable gearing.

The mixer head dismantles easily for cleaning.

The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view, partly in section, showing one embodiment of a mixer head according to the invention together with a motor for driving the same; Figure 2 is a side view, partly in section, illustrating a vertically arranged mixer head; Figure 3 is a partially sectional view of a verti cally arranged mixer head with automatic resinhardener connecting valves; and Figure 4a and 4b are side and end views respec tively of a preferred embodiment of a rotatable screw of a mixer head according to the invention.

Figure 1 shows a mixer head 1 which comprises a mixing chamber 2, horizontally or vertically arranged, provided with a rotatable screw 3 having a helical thread 9 drivable by a motor 4 of a metering machine 5 to which the mixer head is attached.

The mixer head 1 is provided with inlets 6 and 7 for feed of for example hardener and resin respectively. The chamber 2 terminates in an outlet 8.

The motor 4 is an air motor controlled by an air balance valve which is activated by an operating handle of the metering machine. This ensures that the mixer only rotates when materials are being fed into it, thereby preventing overheating of the materials or cavitation which could aerate the mixture. Air-free mixed materials thus emerge from the nozzle outlet 8 at the front end of the mixing chamber 2.

Figures 2 and 3 illustrate vertically arranged mixer heads, wherein the same reference numerals as used in Figure 1 are used to indicate like components. It is envisaged that the invention will be particularly applicable to vertically arranged mixer heads.

Figure 4 shows a preferred embodiment of a rotatable screw 13 for use in a mixer head according to the invention, the screw 13 having a thread 19 which may be of single or multi-start form. The thread 19 has a series of cuts 20 to permit a degree of back flow of the materials being mixed.

This relieves suction at the material inlets which can otherwise cause cavitation, or even override the spring action of one-way check valves on the dispenser, thereby upsetting the metered mixing ratio. However, the overall effect is to feed the components in a generally forward direction, e.g.

vertically, to achieve the same benefit as is described previously.

The rotatable screw is preferably a double start screw with reverse cut helix, to ease suction.

While it is envisaged that for different materials such as pastes etc., the pitch, the number of starts, and the cuts could all be varied, a preferred screw has a 24 mm diameter and has a two-start thread with six helical cuts spaced around the diameter.

The cuts in the thread are preferably cut to the root diameter of the screw.

The screw 13 has an angled tip 21 slotted at 22 to the apex thereof for material discharge. The angled screw tip is slotted to allow the material which is mixed to pass into the discharge nozzle at the end of the mixer head.

Claims (13)

1. A mixer head for attachment to a metering or dispensing machine, comprising a mixing chamber containing or provided with a rotatable screw thread and having inlet means for the components to be mixed and an outlet means for the mixed material.

2. A mixer head as claimed in claim 1, including a rotatable screw provided with a helical thread having a series of cuts therein, to permit back flow of the materials being mixed.

3. A mixer head as claimed in claim 2, wherein the said thread is in the form of a double-start helix and has six helical cuts spaced around the diameter.

4. A mixer head as claimed in any of claims 1 to 3, wherein the said screw has an angled tip slotted to the apex thereof, for material discharge.

5. A mixer head as claimed in any of claims 1 to 4, comprising a mixing chamber provided with a rotatable screw having a helical thread, two inlets adjacent one end of the mixing chamber for infeed of materials to be mixed, and an outlet at the other end of the mixing chamber for discharge of the mixed material.

6. A mixer head according to claim 1, substantially as herein described with reference to, and as shown in, any of the Figures of the accompanying drawings.

7. A metering or dispensing machine to which is attached a mixer head as claimed in any of claims 1 to 6.

8. A machine as claimed in claim 7, wherein the mixer head is vertically arranged.

9. A machine as claimed in claim 7 or 8, wherein the rotatable screw of the mixer head is arranged to be driven by a motor of the said machine.

10. A machine as claimed in claim 9, wherein the said motor is an air motor controllable by an air balance valve activatable by an operating handle of the said machine.

11. A method of mixing multi-component polymer systems, comprising feeding at least two components to be mixed to a mixer head as claimed in any of claims 1 to 6, and rotating the screw thread to mix the said components and convey the mixed material to the mixing chamber outlet.

12. A method as claimed in claim 13, wherein the said components to be mixed are a resin component and a hardener component.

13. A method according to claim 11, substantially as herein described with reference to any of the Figures of the accompanying drawings.