Second-hand cement paper bag machine purchase guide to avoid pitfalls: risk points and precautions

Release time：2025-08-30 Classification：Knowledge

In the cement packaging industry, paper bag machines are a core piece of production equipment. For businesses with limited budgets or those just starting out, purchasing used equipment can be a practical option. However, the used market is fraught with pitfalls. Lack of experience can easily lead to pitfalls, which not only waste money but can also impact production and even create safety risks. This article, drawing on industry experience, will identify key risks and considerations when purchasing used cement paper bag machines to help you make an informed decision.

1. Understand device types and technology evolution

Cement paper bag machines are mainly divided into two categories: bottom gluing machines and bottom sewing machines . The two have different processes and equipment structures. In recent years, with the advancement of technology, multi-station, automation, and intelligence have become the mainstream. Before purchasing second-hand equipment, be sure to clarify:

  1. Process compatibility : Does your product use the paste-bottom process or the sewing-bottom process? Different processes have different equipment requirements. Mixing them will lead to low production efficiency or even failure to produce.
  2. Technology gap : Older models (e.g., over ten years old) may have low efficiency, high energy consumption, poor stability, and discontinued parts, making repairs difficult. Despite attractive prices, the overall cost-effectiveness may be low.

2. Core component inspection: the top priority

The quality of second-hand equipment can be refurbished, but the wear and tear of core components cannot be concealed. You must personally inspect it on site, focusing on the following points:

1. Mechanical structure

  • Frame and foundation : Check for cracks, deformation, and traces of welding repairs. Use a level to check whether the foundation platform is flat. Severe deformation can cause misalignment of components and accelerate wear.
  • Transmission system : Open the gearbox and inspect the gears for wear. Check whether the tooth tips are rounded, pitting, or broken teeth. Check the chain and belt for looseness and aging. Check the main shaft for radial runout and excessive bearing wear.
  • Cam mechanism : Paper bag machines utilize a large number of cams to achieve precise movements. Check the cam profile for significant wear and ensure the roller bearings are flexible and free of play. Worn cams can cause erratic timing and incorrect bag shapes.

2. Electrical control system

  • PLC and inverter : Check the brand and model to determine if they have been discontinued. If a discontinued model fails, repair or replacement costs are extremely high, and the program may be lost. Power on the PLC for a test, observing whether the PLC indicators are functioning normally and any abnormal alarms.
  • Servo systems and stepper motors : These are key to precise positioning. Manually rotate the motor shaft to feel for even resistance. Power on the motor for a test, listening for any unusual noises and observing for accurate positioning and any jitter.
  • Sensors and detection switches : Photoelectric and proximity switches are the "eyes" of the equipment. Check whether they are loosely mounted, whether their surfaces are clean, and test whether their signal response is sensitive and reliable. Failed sensors can cause frequent, unexpected shutdowns.

3. Pneumatic system

  • Check the cylinder barrel for scratches and the piston rod for rust or bending. Check the solenoid valve for crisp movements and leaks. Older equipment's air connections and hoses are prone to aging and leaks, leading to unstable pressure, weak movements, or even inaction.

4. Forming and heat sealing system (for bottom gluing machine)

  • Heat sealing plate : Check whether the surface is flat and whether the coating has fallen off. Check whether the temperature is uniform and controllable, which is the guarantee of sealing strength.
  • Moulds such as formers and folding tools : Check whether the working edges are bumped or worn, and whether the installation position can be flexibly adjusted. Worn moulds will lead to irregular bag shapes and poor openings.

3. Test the machine to verify: Don’t look at the advertisement, look at the effect

No matter how good the static inspection is, it is necessary to conduct a test with material . This is the only way to test the performance of the equipment.

  • No-load operation : Listen to the sound. Check whether the operation is smooth and whether there are periodic impacts or friction noises. Observe whether there are any abnormal vibrations in various parts.
  • Load operation : Use your own base paper or paper of equivalent weight to make bags. Run continuously for at least 30 minutes.
    • Efficiency : Measure whether the actual production speed is consistent with the nominal value.
    • Yield rate : Check the produced paper bags, focusing on: dimensional accuracy (length and width deviation), sealing effect (whether the bottom is firmly glued and there is no glue leakage; whether the bottom seam traces are neat and there are no broken threads), opening quality , and appearance (whether there are obvious scratches or stains).
    • Stability : Observe whether there are frequent paper jams, machine adjustments, and unexplained shutdowns during operation.

IV. Source and background check: Avoid buying a "problematic device"

  • Clear Source : Whenever possible, purchase directly from a factory still in operation. This type of equipment is generally well-maintained and its operating condition is clear. Be extremely cautious with equipment from closed factories, long-term idle equipment, or equipment that has been through multiple transfers, as hidden defects may exist.
  • Original data : Request the equipment's manual, electrical drawings, and PLC program backups . Without these, subsequent maintenance and commissioning will be difficult.
  • Parts compatibility : Confirm whether drawings or suppliers are available for special and non-standard parts (such as gears and cams of special sizes) on the equipment. Otherwise, a damaged part may cause the entire machine to fail.

V. Common Pitfalls and Risk Warnings

  1. Refurbished machines : These have only been painted and cleaned, with internal wear parts not replaced. They are considered "beautification machines." Be sure to peel back the glossy exterior to see what's inside.
  2. Assembled machines : Made from scrapped machine parts of different brands and models. The compatibility of the parts is poor, accuracy is out of the question, and the failure rate is extremely high.
  3. Obsolete model machine : The equipment itself may not have any major problems, but its control system and core components have been completely eliminated, and there are no substitutes on the market, making it a disposable device.
  4. False production capacity : Sellers often quote the theoretical maximum speed of the equipment, but actual production may not reach this limit due to factors such as paper and environmental factors. Always verify actual production performance during a trial run.
  5. Hidden dangers : For example, internal cracks in the frame may have been welded after a major impact, or there may be a short-circuit risk in the electrical circuits after informal modifications, which are difficult for non-professionals to detect.

VI. Negotiation and Delivery Considerations

  • Price evaluation : There's no standard price for used equipment. Consider factors such as the equipment model, year of manufacture, actual condition, technological advancement, and market demand. Consult with industry experts or a third-party evaluation agency.
  • Technical handover : The contract must clearly state that the seller is responsible for disassembly and installation guidance of the equipment, and provides at least 1-2 days of on-site installation and commissioning technical support until qualified products can be produced stably.
  • Spare parts list : Receive spare parts (such as molds, belts, bearings, sensors, etc.) along with the equipment, which is a considerable fortune.
  • Payment method : Avoid paying the full amount at once. It is best to use the "deposit - delivery and inspection - balance payment" method to protect your own rights and interests.

Purchasing a used cement paper bag machine is essentially a game of professionalism, patience, and caution. It requires decision-makers to understand not only price but also the technology, processes, and industry. Remember the old saying: "A cheap old ox may spoil the land." The biggest risk isn't the price, but the enormous opportunity cost and endless repair costs associated with a machine that doesn't function properly. Bring along your most technically knowledgeable engineer and spend ample time inspecting and testing the machine. Pay this "tuition fee" before, not after, the purchase.