Matlhatsi Ntoko Lucas, du Preez Sonette, Van Der Merwe Cornelius J, Linde Stephanus J L
Occupational Hygiene and Health Research Initiative (OHHRI), North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom, 2520, South Africa.
Ann Work Expo Health. 2025 Apr 24;69(4):429-441. doi: 10.1093/annweh/wxaf010.
Occupational exposure to respirable crystalline silica (RCS) is a known cause of respiratory diseases, such as silicosis and lung cancer. Binder jetting additive manufacturing (AM) uses silica sand coated with sulphonic acid as feedstock material and operators are potentially exposed to RCS during various activities associated with AM. This includes the cleaning of the AM machine and associated equipment. This study aimed to investigate particulate exposures associated with additive manufacturing of sand moulds and its preceding silica sand coating process.
The particle size distribution (PSD) and particle shape analysis of different forms of silica sand (virgin, coated, and used) was determined using a Malvern Morphologi G3 automated microscope and the structural characteristics was measured using X-ray diffraction (XRD). Personal exposure and area monitoring for airborne respirable dust and RCS were performed using MDHS 14/4 and NIOSH 7602, while real-time particle number concentrations of 0.3 to 10 µm sized particles was measured using the TSI Aerosol Particle Counter (APC). Monitoring was performed for 2 operators over 8 d and included 3 d of coating, one day of cleaning the AM machine, and 4 d of printing during which 3 identical parts were manufactured.
According to the PSD analysis, virgin and used silica sand particles were mostly in the respirable size range (d(0.9) = 3.98 ± 0.72 µm; and d(0.9) = 6.51 ± 2.71 µm, respectively), while coated sand was mostly in the inhalable size fraction d(0.5) = 29.76 ± 42.91 µm). The wt% results of the XRD analysis for the bulk virgin, coated and used silica sand were 97.3%, 92.6%, and 96.8% quartz, respectively. Personal exposure to RCS exceeded the exposure limit of 0.1 mg/m3 when the operator used compressed air to clean the coating machine's filter (0.112 mg/m3) and exceeded the action level on the day the AM machine was cleaned (0.70 mg/m3). The results for real-time particle number concentrations of 0.3 to 10 µm sized particles showed peaks while the cleaning activities such as dry sweeping were performed.
The personal exposure to RCS was the highest on days when cleaning activities that used compressed air and dry sweeping took place. The high quartz content of the silica sand feedstock material and the respirable size of the virgin and used silica sand particles means that cleaning activities pose an RCS exposure risk to AM operators. Nine recommendations are made to reduce exposure to RCS during cleaning activities.
职业性接触可吸入结晶二氧化硅（RCS）是矽肺病和肺癌等呼吸系统疾病的已知病因。粘结剂喷射增材制造（AM）使用涂有磺酸的硅砂作为原料，在与增材制造相关的各种活动中，操作人员可能会接触到RCS。这包括增材制造机器及相关设备的清洁。本研究旨在调查与砂模增材制造及其之前的硅砂涂层工艺相关的颗粒物暴露情况。
使用马尔文Morphologi G3自动显微镜测定不同形态硅砂（原生、涂层和使用过的）的粒度分布（PSD）和颗粒形状分析，并使用X射线衍射（XRD）测量其结构特征。使用MDHS 14/4和美国国家职业安全与健康研究所（NIOSH）7602方法对空气中可吸入粉尘和RCS进行个人暴露和区域监测，同时使用TSI气溶胶颗粒计数器（APC）测量0.3至10μm大小颗粒的实时颗粒数浓度。对2名操作人员进行了8天的监测，包括3天的涂层、1天的增材制造机器清洁以及4天的打印过程，在此期间制造了3个相同的部件。
根据PSD分析，原生和使用过的硅砂颗粒大多在可吸入粒径范围内（d(0.9)分别为3.98±0.72μm和6.51±2.71μm），而涂层砂大多在可吸入粒径范围d(0.5)=29.76±42.91μm）。原生、涂层和使用过的块状硅砂的XRD分析重量百分比结果分别为97.3%、92.6%和96.8%的石英。当操作人员使用压缩空气清洁涂层机过滤器时，个人对RCS的暴露超过了0.1mg/m³的暴露限值（0.112mg/m³），并且在增材制造机器清洁当天超过了行动水平（0.70mg/m³）。0.3至10μm大小颗粒的实时颗粒数浓度结果在进行干扫等清洁活动时出现峰值。
在进行使用压缩空气和干扫的清洁活动当天，个人对RCS的暴露最高。硅砂原料的高石英含量以及原生和使用过的硅砂颗粒的可吸入粒径意味着清洁活动会给增材制造操作人员带来RCS暴露风险。提出了九条建议以减少清洁活动期间对RCS的暴露。
