GB2074051A - Coating of pipes with plastics material - Google Patents

Abstract

Pipes are coated with plastics material by loading the pipes onto an indexing conveyor on which they are presented to a series of successive stations 21-24. Each pipe is successively heated by burner 35, coated with powdered plastics material by hopper 29 and then quenched in water bath 39 before being removed from the conveyor. The pipes are rotated on the conveyor whilst at the heating and coating stations 21, 22. <IMAGE>

Description

SPECIFICATION Coating of articles with plastics material Technical field In various engineering fields it is necessary to coat with plastics material the surface of generally large objects, for example lighting columns and conduits.

Such a coating is necessary to protect the article against corrosion and other environmental attack and also to give the article a decorative appearance.

Background art A previously proposed method of coating articles in plastics material comprised heating the article in an oven, spraying on primer and then immersing the article in a fluidised bed of powdered plastics material. While the process produced acceptable coatings on articles it was costly to use in that up to six men were needed to convey the articles through the process. The process had further disadvantages when used with lighting columns which have inspection doorways cut at their base. With such columns a considerable amount of particulate material entered the column resulting in plastics wastage and loss of time where the hardened material had to be removed.

It is therefore an object of this invention to provide a coating process where the above disadvantages are minimised.

Invention Apparatus for coating an article with plastics material comprising: an indexing carrier for presenting the article successively to one of a plurality of positions, a heat source, a dispenser for powdered plastics material and a cooling bath each adjacent a respective one of said positions, and means for rotating the article when at the positions adjacent the heat source and the dispenser.

Preferably the carrier comprises a plurality of arms extending from a common axis, the ends of the arms remote from the axis being adapted to support an article to be coated, such as a pipe.

The arms of the carrier may be arranged in two similar cruciforms each centered on the axis, the article to be coated being supported between a pair of corresponding arms, one on each cruciform.

The invention also provides apparatus for dispensing powdered plastics material onto the surface of an article comprising a hopper having a bottom slot for the discharge of plastics powder and a flowdivider extending adjacent and below the slot whereby the flow of powder from the slot is split by the flow-divider into two discrete paths.

For a fuller understanding of the invention reference will now be made by way of example to the accompanying diagrammatic drawings in which: Figure 1 is a plan view of an apparatus for coating articles with plastics material, Figure 2 is a sectional view taken in direction 2-2 of Figure 1, Figure 3 is a detailed side view of the apparatus taken in the direction of arrow 3 in Figure 2.

Figure 4 is an end view of the apparatus taken in the direction of arrow 4 in Figure 1, Figure 5 is a detailed perspective view of a plastics material hopper.

The apparatus comprises an indexing carrier which comprises two cruciform supports 10 and 11 each rotatably mounted on axle 12. The arms 13 of support 10 are pivotably mounted on boss 14 so that they are movable under the action of pneumatic piston and cylinder assemblies 15 in the direction of arrows 16. The arms of support 11 are rigidly mounted on boss 16. Atthe outer end of each of the arms 13 and 17 is a frustro-conical member 18 for engaging the open ends of a pipe 19 which is to be coated.

The supports 10,11 are driven by means not shown for stepped rotation through 90" increments in the direction of arrow 20 (Figure 2) so that each support adopts successively positions 21,22, 23 and 24. At position 22 the member 18 on arm 17 engages a drive mechanism 25 driven by motor 26 through belt 27. The drive mechanism 25 causes the member 18 and its associated pipe 19 to rotate about axis 28.

At position 21 there is provided a gas burner unit 35 which comprises a number of independently controllable burners 35 which project a jet of flame on to the pipe at position 21 which is rotated while at this position by drive means 38.

The strength of each burner may be varied to accomodate variations in the shape of the article to be coated so that the whole article is heated to a uniform temperature.

Associated with position 22 of the apparatus there is a hopper assembly shown generally 28. The assembly comprises a hopper unit 29 through a mesh screen in the bottom of which is dispensed plastic powders (e.g. polyvinylchloride (p.v.c.), nylon, etc.). A tray 30 is located beneath hopper 29 to catch any excess p.v.c. The hopper 29 and the tray 30 are joined together by a frame 31. The hopper assembly 28 is pivotably mounted at the end of arms 32 which are themselves pivotably mounted on pivots 33. Rotation of arms 32 about pivots 33 in the direction of arrow 34 causes the hopper assembly to be swung towards or away from position 22.

The hopper 29 is oscillated in the direction of arrow 36 by drive mechanism 37. (Figure 5).

Any excess plastics powder in the tray 30 is recycled into the hopper unit 29. Thus wastage of powder is minimised At position 23 on the apparatus there is a water bath 39.

In operation, where a pipe is to be loaded on to the apparatus at position 24, the piston and cylinder unit 15 is actuated to move arm 13 back in the direction of arrow "A". An end of a pipe to be coated is fitted on to member 18 on arm 17 and them arm 13 is actuated to move back and insert member 18 into the other end of the pipe. The pipe is thus secured between arms 13 and 17.

The supports 10 and 11 are then rotated through 90" to bring the pipe to position 21. The pipe is then rotated beneath the gas burners until its temperature reaches a temperature beyond the melting point of the plastics powder.

The supports 10 and 11 are then further rotated to bring the pipe to position 22. The hopper assembly 28 is then swung into the position shown in Figure 2.

When the assenbly is in position the pipe is rotated and powder is dispensed from hopper 29 while this is oscillated in the direction of arrow 36. The rotation of the pipe and the osciliation of the hopper ensure an even coating of powder on the pipe's exterior surface. The powder then melts to form a continuous coating on the surface of the pipe.

When the coating operation is complete the hopper assembly 28 is swung away in the direction of arrow 34 to allow the pipe to be progressed to position 23 where it is immersed in water bath 39 whereupon the plastic coating solidifies. The pipe is then brought to position 24 where it is removed and afresh pipe is loaded onto the apparatus. It will be seen that in operation a coated pipe is removed and a fresh pipe is loaded after each 90" step revolution of the apparatus.

Figure 3 shows a detail of the hopper 29 for use where the apparatus is intended to coat articles such as lighting columns which have openings cut in their length.

Below the hopper 29 a right-angle section flowdivider 40 is secured with the right angles apex 41 uppermost. The dimension 42 across the base of the flow-divider 40 is chosen to correspond closely with the dimension 43 of an opening 44 in the lighting column 45 to be coated. Thus there results beneath the flow-divider 40 two curtains 46 of p.v.c. powder each spaced an equal distance 47 from the longitudinal axis 48 of the column. Thus, at the point in the revolution of the column where the opening 44 is uppermost the spacing of the curtains 46 is such that the falling powder coats the sides of the column with little entering the opening. At positions immediately before and after the highest position of the opening 44 the slight sideways component of movement of the falling powder imported by the flow-divider 40 causes the powder to coat the side edges of the opening 44.Edge 49 is coated at approximately position 50 in the rotation of the column while edge 51 is coated at position 52.

At positions in the region of 50 and 52 a small quantity of powder does enter the opening but this is far less than would enter in the absence of flowdivider 40. However, the oscillatory movement of the hoper imparts a component of movement to the falling powder in the direction of arrow 53. This movement of powder causes upper and lower edges 54, 55 of the opening to be coated. Thus the arrangement of flow-divider 40 on an oscillating hopper causes the edges of a wide variety of shapes of opening to be coated.

In addition to coating articles in p.v.c. the apparatus is suitable for coating in nyion and polyethylene or like plastics material.

The thickness of the coating is readily controlled by determining the number of revolutions of the article under the hopper unit 29. In each case an even coating results due to the rotation of the article.

As the hopper unit contains a relatively small quantity of powder relative to a fluidised bed it is easier to change the material used in the coating process e.g. by merely exchanging the hopper unit 29.

One of the cruciform supports may be arranged to slide along its rotational axis so that articles of varying lengths may more readily be accommodated.

Claims (6)

1. Apparatus for coating an article with plastics material comprising: an indexing carrier for presenting the article successively to one of a plurality of positions, a heat source, a dispenser for powdered plastics material and a cooling bath each adjacent a respective one of said positions, and means for rotating the article when at the positions adjacent the head source and the dispenser.

2. Apparatus as claimed in claim 1 wherein the carrier comprises a plurality of arms extending from a common axis, the ends of the arms remote from the axis being adapted to support an article to be coated, such as a pipe.

3. Apparatus as claimed in claim 1 or 2 wherein the arms of the carrier are arranged in two similar cruciforms each centred on the axis, the article to be coated being supported between a pair of corresponding arms, one on each cruciform.

4. Apparatus for dispensing powdered plastics material onto the surface of an article comprising a hopper having a bottom slot for the discharge of plastics powder and a flow-divider extending adjacent and below the slot whereby the flow of powder from the slot is split by the flow-divider into two discrete paths.

5. Apparatus as claimed in claim 4 further comprising means to oscillate the hopper generally in the direction of the longitudinal axis of the slot.

6. Apparatus for coating an article with plastics material substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings.