FR2616706A1 - PROCESS FOR PRODUCING A RESERVOIR SUCH AS A FUT - Google Patents

Abstract

The reservoir consists of a metal outer shell 1, 2, 3 and an adherent inner shell 10 produced by rotational molding from a thermoplastic material capable of undergoing shrinkage after molding and, after molding and removal of this shell, an elastomeric resin is injected between the outer casing 1, 2, 3 and the inner casing 10 so as to fill the space 11 created between these casings and to secure them on all their facing surfaces.

Description

-21 - Method for producing a tank such as a barrel

  The invention relates to a method for producing a

  tank such as a barrel made of a metal outer casing-

  lique and an adherent internal envelope in thermoplastic material--

tick produced by rotational molding.

  For the transport of products such as chemicals, it is common practice to use tanks such as drums made of metal when the nature of the packaged product allows. On the other hand, when the packaged product is corrosive or when the purity of the packaged product must be preserved, the use of metal drums often proves to be ineffective. To remedy this situation, it is possible to envisage the use of metal tanks whose internal wall is coated with an inert thermoplastic material or guaranteeing the

  preservation of the degree of purity of the product to be packaged.

  In the latter case, a particularly interesting solution-

  health can consist of internally coating the surface of a tank with a layer of inert thermoplastic material deposited by the rotational molding technique using the tank

metallic as mold.

  However, when operating according to this technique, it is generally found that after the rotational molding operation, the internal envelope of thermoplastic material undergoes a significant shrinkage which has the effect of separating it from the external metallic envelope. A tank is therefore obtained in which the internal envelope can freely float in the external envelope, which in particular entails risks of deterioration

  of this internal envelope during subsequent handling.

  The present invention relates to a method for producing a reservoir such as a barrel consisting of a metallic outer shell and an inner shell produced by rotational molding at - 2 -

  from a thermoplastic material which no longer leads to in-

  agrees above. It also allows the production of tanks having a remarkable impact resistance and which can

  withstand internal pressures of up to 2 MPa.

  The present invention therefore relates to a method for producing a reservoir such as a barrel consisting of a metallic outer shell and an adherent inner shell produced in the metallic shell by rotational molding from a subject thermoplastic material, after molding. , a shrinkage which separates it from the metal envelope in which, after molding and removal of the internal envelope, an elastomeric resin is injected between the external envelope and the internal envelope so as to fill the space created between these envelopes and to be joined

  these on all their facing surfaces.

  The reservoir according to the invention can be in any form: container, barrel, can, etc. and the outer casing can be made of any metal, mild steel being generally preferred. This outer casing can be made in one piece, for example by the stamping technique, or be made up of several pieces connected together by welding or crimping. When the tank is a barrel, the external envelope may be provided with filling and / or draining tips, possibly protected by

metallic skirts.

  To carry out the process according to the invention, it is however necessary to provide an orifice with a diameter of 5 to 10 mm in one of the bottom parts of the metal casing, as well as a vent with a diameter substantially equal in other background

of the metal casing.

  The thermoplastic material used to make the envelope

  internal mold by rotational molding can be arbitrary and

  present in the form of a plastisol or in the form of a powder.

  This thermoplastic material can be a vinyl resin such as polyvinyl chloride or polystyrene, an olefin resin such as low or high density polyethylene, polypropylene, an acrylic resin or a fluorinated resin.

  such as for example polyvinylidene fluoride or a copoly-

  mother of vinylidene fluoride, this last resin, counts

  given its high chemical inertness, being preferred by the demand

  for the creation of tanks for packaging

  of products whose purity is to be preserved.

  To produce the reservoir according to the invention, the metallic external envelope is used as a mold for the rotational molding of the internal envelope, the material constituting this internal envelope being generally introduced in the pasty, pulverulent or granular state by one of the openings of the metallic outer casing. It is also obvious that before proceeding with the rotational molding operation, it is advisable to temporarily close all the openings provided in the metallic outer casing, for example by means of plugs. Since the rotational molding technique is well known, it need not be described in detail. For all information on this subject, reference is made in particular to the work "Rotationsschmelzen und Schleudergiessen von Kunststoffen" by H. Becker, W.E. Schmitz and G.W. Weber, Edition Carl Hanser Verlag Munich 1968 which is

  incorporated by reference in the present description.

  In the process according to the invention after molding and removal of the internal envelope, an elastomeric resin is injected, through the opening provided in the external metallic envelope, between the external envelope and the internal envelope so as to fill the space created between these envelopes and secure them on

all their facing surfaces.

  This injection can be carried out by means of an injection press or by means of a pump, the injection pressure

being between 0.1 and 2 MPa.

  During the injection of the elastomeric resin, it may prove advantageous to maintain the envelope under a vacuum of 75,000 to 150,000 Pa absolute. This vacuum effect results in a contraction of the internal envelope and thus

2 616706

  - 4 - facilitate the filling of the space between this

  shell and the metallic outer shell.

  The elastomer resin injected can be of any material such as, for example, polyurethane resins, epoxy resins, silicone rubbers, "alkyd" resins, unsaturated polyesters, phenol and formaldehyde resins, silicone resins, polyamides such as nylon 6 and resins generated from styrene and / or methyl methacrylate. In general, it is preferred to use a resin which does not lead to cellular structures and which has good adhesion properties on the materials constituting the

  outer and inner shell of the tank. In general, the request

  deresse prefers to use polyurethane resins.

  After filling the space between the envelopes with the elastomeric resin, it proves useful to release the vacuum created in the internal envelope and to fill the latter with a liquid such as water at a temperature between 20 and 60 C during the setting of the elastomeric resin and, preferably, during a

duration of 24 to 60 hours.

  After this period of time, it is enough to empty the tank and unclog the orifices of the metallic outer casing to

  get a ready to use tank.

  The method according to the invention is further illustrated by the practical embodiment which follows and which relates to the production of a barrel with a capacity of 200 liters which is particularly suitable for the packaging of products whose

wishes to maintain purity.

  In the description of this example, we refer to the figure

  unique drawing attached which represents in section such a barrel after

  rotational molding and cooling of the internal envelope.

  As can be seen in FIG. 1, the barrel consists of an external metallic casing comprising a side wall 1 consisting of a curved and welded ferrule made of 4 mm mild steel

  thick, and two added and welded ends 2 and 3 equal

  made of mild steel 4 mm thick, the upper bottom 2

- 5 -

  comprising two filling and / or emptying nozzles 4.5.

  The outer casing also includes two attached skirts 6 and 7 which protect the end pieces 4 and 5 against shocks

  as well as the vertical stability of the external envelope.

  Furthermore, the bottom 3 and the bottom 4 each have an opening 7 and 8 of 6 mm in diameter, each opening being able to be closed temporarily by a plug, not shown. After closing the opening 8, 18,000 g of polyvinylidene fluoride resin in the pulverulent state are introduced into the external envelope by one of the nozzles 4, 5, then

closes openings 4, 5 and 9.

  Then, the rotational molding operation is started by bringing the outer casing to a temperature of 285 ° C. and subjecting it to appropriate rotational movements so as to

  cause formation against the inside of the metal casing-

  polyvinylidene fluoride inner shell

  continuous with a uniform thickness of 4 mm.

  After cooling the assembly for 48 hours, it can be seen, as shown in FIG. 1, that the inner casing 10 of polyvinylidene fluoride has undergone a greater shrinkage than the outer casing and that a space has formed

11 continuous between these envelopes.

  In accordance with the process according to the invention, the openings 4, 8 and 9 are opened and via the opening 4, a slight vacuum is created (93,000 Pa absolute), then via the opening, an elastomeric polyurethane resin is injected into the space 11 located between the inner 10 and outer envelopes, the injection carried out under a

  pressure of 0.59 MPa being continued until this -

  resin appears at the opening 9. The poly-

  elastomeric urethane used is obtained from Ka Cepol WS 555 (polyether triol produced and marketed by the company Kali-Chemie AG) and diphenylmethane-4,4'-diisocyanate, the agent

  crosslink being 1,4-butanediol.

  The internal envelope 10 is then filled with water at

- 6 -

   C and after 48 hours, the internal envelope is emptied.

  The barrel thus obtained is ready for use and is particularly suitable

  especially for packaging aggressive products or products whose purity is to be maintained. It is also characterized by remarkable impact resistance. Finally, the barrel perfectly withstands an internal pressure of 1.6 MPa and allows

pressure emptying.

-7-

RE V E N D I C AT I 0 N S

  1 - Method for producing a reservoir such as a barrel consisting of a metallic external envelope and an envelope

  internal adherent produced in the metallic envelope by roto-

  molding from a thermoplastic material undergoing, after molding, a shrinkage which separates it from the metal casing, characterized in that after molding and removal of the internal casing, an elastomeric resin is injected between the external casing and the internal envelope so as to fill the space created between these envelopes and to join them together on all of their

facing surfaces.

  2 - Method according to claim 1, characterized in that

  that the elastomeric resin is injected through a prior orifice-

  ment provided in a bottom part of the metal casing, a vent being generally provided in the other bottom part of the

the metal casing.

  3 - Method according to claims 1 or 2, characterized

  in that the injection pressure of the elastomeric resin is

between 0.1 and 2.MPa.

  4 - Method according to any one of claims 1

  to 3, characterized in that the internal envelope is maintained under an internal vacuum of 75,000 to 150,000 Pa absolute during

  injection of the elastomeric resin.

  - Method according to any one of claims 1

  to 4, characterized in that after the injection of the elastic resin

  mother, we keep the inner envelope filled with a liquid at a

  temperature between 20 and 60 C for 24 to 60 hours.

  6 - Method according to any one of claims 1

  to 5, characterized in that the internal envelope is produced by

rotational molding of a fluorinated resin.

  7 - Process according to claim 6, characterized in that the fluorinated resin is a resin based on vinylidene fluoride. - 8 -

  8 - Method according to any one of claims 6

  to 7, characterized in that after rotational molding of the envelope in

  fluorinated resin, an elastomeric polyurethane resin is injected.